Over the green swaths of a manicured lawn, an operator on a zero-turn mower seems to glide along, trimming off the top half-inch of each blade. Through his ear protection, the roaring life of his machine is muffled to a distant thrum, like the buzzing of an active beehive. He’s been using this mower for a year and a half now, but for how well he knows it, he may as well have used it his entire life.

He knows how it sounds in every condition: blades on, blades off, going up slopes, going down slopes, over wet turf and dry asphalt. Today though, something is different. Today, his staid expression shifts as that distant familiar tone leaves the beaten path and signals trouble.

As he hears this new discord, he uncouples the blades and breaks off of his route. Something’s wrong, and now he’s got to get back to the trailer and try to diagnose the problem. Maybe it’s the air filter, maybe it’s the oil, maybe (heaven forbid!) another crew member filled the tank with E-30, and there’s water in the engine.

Whatever the cause, if that mower is kaput, you can bet your bottom dollar that its owner will be making some calls. Maybe he’ll call the dealer who sold it, or the mower’s manufacturer to find out what the problem is, but the call he won’t make is to the company that made the engine itself.

It’s not surprising; still, it raises an interesting point. The mower’s engine is its beating heart, but we don’t often hear from that engine’s creator. Whether trying to diagnose a palpation or trying to figure out if it’s the right size, a mower wears its heart on its sleeve. But without an engineering degree, it can be hard to know whether it’s the right heart for the job.

This isn’t some abstract philosophy question, either. A mower that has too much power is using more fuel than it has to, and a mower without enough power is working slower than it could be. Either way, the impact will play itself out on the company checkbook, so it’s worth looking into. Do you know what’s putting the power in your power equipment?

Engines, like engineers, have their own language, a language of physics formulas that translate into power and efficiency. If you want to know what your motor is saying, you have to speak that language.

Let’s start with torque. Torque is a measure of how much force an engine can put out, usually measured in foot-pounds. A mower with lots of torque can cut through high, thick grass that might stymie a machine without as many foot-pounds. “If you don’t have enough torque and you’re cutting six inches of grass, then your engine’s going to start slowing down all of a sudden,” said Eric Raquet, product manager for gas engines, the Kohler Company in Kohler, Wisconsin.

Using a low-torque machine is like replacing your mower’s blades with razors. They might be sharp and fast, but the second they face any resistance, you’re in trouble. Most mower engines have plenty of torque for their intended uses; however, it’s something to keep in mind when buying a machine that’ll see heavy use. For a frame of reference, 50 foot-pounds is probably the maximum amount a mower needs, and should be enough for all but the widest decks in the wettest conditions.

Of course, the most commonly quoted stat for an engine is horsepower (hp), but what does that really mean? Horsepower is torque multiplied by rotations per minute, so it’s a measure of how much work your engine is actually doing as you run it. It was invented in the 18th century to explain to farmers how much power a steam engine had.

Nowadays, most people can’t picture how much work one horse can do, let alone 100. There are some ballpark estimates for the power needs of mowers, which you can use as guidelines.

“A 60-inch deck needs maybe 27 horsepower, and it ramps down from there,” said Raquet. “I would say that once you start getting to a 54- inch or a 48-inch deck, you can start coming down to 25, 24 or 23 hp.” Deck width is just one variable among many when it comes to power requirements; mower type can be a factor, too.

Walk-behind mowers will need less power than stand-ons or zero-turn machines. By the time you get down to a 20-inch walk-behind mower for manicuring, 3 or 4 hp is probably more than enough.

On the other hand, if you intend to make use of mower attachments, you’ll probably need more power for those applications than the stock machine uses. Ultimately, it’s important to remember that you’re the best judge of your own needs, and so the easiest way to know whether a mower has enough power is to try it out yourself.

It’s also important to realize that not all horsepower figures are created equal. When presenting their engine lineups, all companies are giving you the maximum output, but some use the gross horsepower, and some give net horsepower instead.

You may even find listings that use a third power measurement. “Some use torque-power, which is a formula of horsepower and torque put together,” said Michael Rickey, senior manager with Honda engines. “Does that really give a customer a true vision of what that engine will put out? I’m not sure.”

Gross horsepower refers to an engine’s maximum hp under ideal conditions, while the net horsepower is closer to an engine operating under its intended load. The two terms are holdovers from the automotive industry, where the differences between them are proportionately greater.

They were once used by marketers to influence consumers and racing organizations. Since then, the car companies have cleaned up their act, and the two numbers are much closer together. Engines are typically tested using the latest standards published by the Society of Automotive Engineers (SAE).

The two tests you’re most likely to see are J1349 and J1995, which are small engine tests for net horsepower and gross horsepower, respectively. If you see J1940 instead, know that it’s just an umbrella number for those two tests. The real measure of a machine is how well it works when you use it, but horsepower derived under the same testing conditions should be equitable.

Getting that number right isn’tjust important for the manufacturer, it’s important for you, too. As always, power comes with a price, and in this case, it’s paid at the pump. An engine with too little horsepower costs you productivity, but an engine with too much horsepower is using more fuel than you need. Fortunately, recent advancements have led to engines that give the operator only the exact power that they need, and only when they need it.

Electronic Fuel Injection, or EFI, has been a major buzzword among manufacturers of mowers and engines alike for the past few years, and with good reason. I spoke with some engine manufacturers to see how this new advance is improving machines.

The first benefit is the mechanical advantage of injection. Spraying fuel into a cylinder is more efficient than squirting it. “Normally, you’re squirting fuel into that chamber, which is fairly imprecise, all things considered,” said Jim Cross, marketing manager, commercial engines for Briggs & Stratton in Milwaukee, Wisconsin. “With EFI, the fuel is atomized and sprayed into the cylinder in a very precise manner, and at the proper ratio to optimize that explosion.”

Optimizing a cylinder’s explosion may seem like simple math, but the real world is a lot messier than the lab, so the process only begins there. The Electronic Control Unit (ECU) of an EFI engine compensates for all sorts of adverse conditions, both external and internal. B y accounting for variables like slope, air pressure, fuel pressure and throttle position, an ECU can give you precise power, no matter what.

Between the atomizing and the ECU’s magic math, engines with EFI can show up to a 25 percent reduction in fuel use as compared to their carbureted cousins. “We have estimated that, depending on gas prices, over the life of the machine you’ll probably spend $10,000 on fuel,” said Raquet. Saving $2,500 per mower is a real boon for any contractor.

Troy Smith, application engineering supervisor at Kawasaki Motor Corporation in Lansing, Michigan, thinks that EFI can offer even bigger savings than just fuel costs. “In a mechanically-governed engine, there’s always a mechanical loss associated with that governor,” he said. EFI provides an opportunity to replace that mechanical system with an electronic one.

An electronic governor allows the machine to maintain a constant speed in any condition. “It gives manufacturers of lawn mowers a better means of designing say, a deck, to a specific rpm, because that rpm isn’t going to change,” said Smith. For the end user, that translates into decreased engine droop, meaning more productivity.

EFI is a major advance in the mower motor market, but it isn’t the only one. Cyclonic air filtration is also making headway. “In a typical filtration system, the air enters the air box and just sits there,” said Cross. “With cyclonic air filtering, first the major debris is chopped up and thrown out. Then the air heads into a chamber where it’s spun around, separating out even more debris.”

All that remains are very fine particles, which get plucked out as the rotated air is passed through an air filter. Because the air filter only has to catch a fraction of the debris, it’s doing less of the work, which, in turn, makes maintenance less frequent.

Another element of engine choice that’s getting more and more consideration is the use of alternative fuels. Gasoline prices over the past decade have been awfully volatile, and some manufacturers have been dipping their toes into propane as a result.

There are kits out there which you can use to retrofit an engine, but doing so may void your warranty. So, if you’re thinking of switching, you might want to look into whether there’s a stock engine that will fit the bill. Some mower manufacturers have their own kits, designed to be used with their mowers.

Ethanol is another major concern, as small engines are particularly sensitive to the biofuel’s water-attracting properties. “There was some legislation recently which was looking into the possibility of increasing ethanol up to 15 percent in gasoline. A lot of small engine manufacturers would have a problem with that,” said Raquet.

In case they do, his company produces a flexfuel engine with EFI that can take up to E-85, the highest ethanol content currently available. Then again, approaches differ. “Alternative fuels are always a possibility, but currently we’re focusing on gasoline,” said Smith.

The design philosophy of the people who make your power plants can tell you a lot about what you can expect from them. Whether you’re thinking of buying a single walk-behind mower, or trying to manage an entire fleet, making an informed decision is important for your business. When it comes to your equipment, there are no small choices.

Smith says their efforts are focused on productivity. “What that results in is you’re getting more productivity out of the engine, more productivity out of the operator, and you end up getting the machine on the trailer, and down to the next job faster.”

For Cross, some of the needs are related. “When you look at cost to operate, you look at ease of service, you look at downtime,” he said. “Cost of operation you can tie to toughness; the machine’s never going to be down.”

Rickey takes a different tack. “Contractors want ease of use, a good warranty, and good infrastructure that’s able to support that product with parts, service and any technical advice,” he said. “That’s an important thing for the contractor, because their livelihood comes from that product.”

“You really want to have high productivity at low cost of operation,” said Raquet. “The needs of commercial landscape contractors are durability, durability and durability.”

When you’re running a business, it can be easy to get swept up by the hundreds of decisions you have to make every day. A landscape maintenance operation lives and dies by its mowers. Those machines have to work day-in, day-out, and nothing is more central to their function than the engine. If you take the time to know your engine options, at least one of those decisions will be straightforward.